Radionuclides provide a noninvasive approach for evaluation of cardiovascular disease. These procedures do not produce all the information obtained from a complete cardiac catheterization and are not anticipated to replace this study. However, the large amount of hemodynamic information available from radionuclide studies which may be repeated serially holds great potential for aiding the initial evaluation and monitoring of treatment of patients with congenital heart disease. In addition to the diagnostic potential of these studies, the physiologic data provided may be used to assess the natural history and to examine hemodynamic alterations resulting from physiologic stress in patients with congenital heart disease. The first specific goal of this investigation will be to refine methods of data manipulation which optimize the pictorial and quantitative description of cardiac function. A multiparameter computer model of the central circulation will be fitted to the radionuclide data to define patterns of abnormal blood flow associated with congenital valvular abnormalities and intracardiac shunts. The mean flow, volume, and transit time of individual cardiac chambers will be calculated. Right and left ventricular volume changes during each cardiac cycle will be imaged and measured and the validity of these measurements will be evaluated by animal experimentation. In addition to more standard agents, cyclotron produced C15O2 administered by inhalation will be examined for noninvasive quantitation of shunts in children with cardiac murmurs. Clinical studies will define physiologic alterations associated with congenital heart disease such as changes in intracardiac shunts with exercise, the influence of surgery on cardiac function, and the quantitation of systemic-to-pulmonary blood flow in cyanotic congenital heart disease. The final objective will be to define the clinical utility of radionuclide procedures in diagnosis and management of patients with these disorders.